1. Field of the Invention
The invention relates to a hydraulic pressure control apparatus of a vehicular automatic transmission and a control method for a hydraulic frictional engagement device of a vehicular automatic transmission, which preferably suppress shift shock when a predetermined upshift is executed by increasing an engaging pressure of a predetermined hydraulic frictional engagement device, by correcting the engaging pressure based on generation of a factor that changes an input torque of the transmission during a power-off upshift.
2. Description of the Related Art
JP-A-2001-124192 discloses a hydraulic pressure control apparatus is known that executes a predetermined upshift by increasing the engaging pressure of a predetermined hydraulic frictional engagement device in a vehicular automatic transmission that shifts speeds by selectively engaging a plurality of hydraulic frictional engagement devices. This apparatus performs the six following steps. In the first step, it is determined whether an upshift being performed is a power-off upshift (i.e., an upshift in which the accelerator pedal is not being depressed). When it is determined in the first step that a power-off upshift is being performed, it is then determined in the second step whether all power-off upshift conditions have been fulfilled. When it has been determined in the second step that all power-off upshift conditions have been fulfilled, the apparatus then measures a fluid pressure response time, determines a maximum duty value so as not to force the transmission to shift, and calculates the fluid pressure response time for when that maximum duty value is changed to 100% in the third step. After the fluid pressure response time is calculated in the third step, a shift complete point is then calculated in the fourth step. In the fifth step, it is determined whether the shift complete point calculated in the fourth is in sync with an actual shift complete point that is based on the actual engine speed and turbine rotational speed. When it has been determined in the fifth step that those two points are in sync, the maximum duty value is set to 100% in the sixth step and the shift ends. Completing the shift so that the calculated shift complete point is in sync with the actual shift complete point based on the actual engine speed and the turbine rotational speed enables undershooting of the engine speed, as well as tie-up which is caused by that undershooting, to be preferably suppressed.
With this hydraulic pressure control apparatus for a vehicular automatic transmission, however, when a factor or the like that changes the output torque of the engine due to operation of fuel cut control or air conditioner control or the like is generated, during a power-off upshift, the rate of change in the turbine rotational speed fluctuates. When that rate of change is large, undershooting of the engine speed is generated at a point near synchronous rotation, such that, during synchronized rotation, there is a sudden feeling of deceleration and shift shock.